This invention relates to an apparatus for growing a semiconductor crystal and a method of growing the same, and in particular, to a crystal growing technique for rotating semiconductor melt (or solution) by applying a magnetic field and current which cross each other in the semiconductor melt.
A semiconductor crystal wafer used as a substrate of a super highly integrated electronic device is generally grown by the use of the Czochralski method (hereinafter, abbreviated as the CZ method).
In the CZ method, the semiconductor crystal wafer is grown by pulling a semiconductor single crystal from a rotating semiconductor melt while rotating the semiconductor single crystal in an opposite direction to that of the semiconductor melt.
With such an arrangement, the semiconductor melt is retained in a crucible which is heated by a cylindrical heater which is arranged around the crucible. Using this arrangement, the crucible is rotated so as to ensure uniform temperature distribution in the semiconductor melt.
To this end, it is necessary that a rotating center of the crucible and a symmetrical axis of heater arrangement correspond to the pull axis of the semiconductor crystal in order to ensure uniform temperature distribution in the semiconductor melt symmetrical with the axis.
In general, the axis for holding the crucible is mechanically rotated in a conventional manner.
However, a large apparatus is required to rotate a crucible used for growing large size crystals. Consequently, the growth of large semiconductor crystals is difficult.
To solve such difficulty, an apparatus for growing a semiconductor crystal and a method of growing the same has been proposed in unpublished Japanese Patent Application No. Hei. 9-343261, which apparatus includes a device for applying a magnetic field to semiconductor melt during growth of a semiconductor crystal and another device for applying current perpendicular to the magnetic field of the semiconductor melt.
Further, an electrode which is immersed in the semiconductor melt and another electrode which supplies current to pull a semiconductor crystal are used in the above semiconductor crystal growing apparatus.
In this semiconductor crystal growing apparatus, even when a semiconductor crystal having a large diameter of 30 cm or more is grown, the size of the apparatus is minimized, and it is possible to accurately control rotation.
However, when electrode material is dissolved in the semiconductor melt and the electrode material contains material other than the semiconductor melt and the growing semiconductor crystal, the purity of the semiconductor melt and the growing crystal is degraded. This produces an adverse affect for the other impunity concentration distribution.
Moreover, when the electrode is immersed into the semiconductor melt, the rotation of the semiconductor melt is partially interrupted by the electrode. As a result, symmetry of the rotation is also degraded.
It is therefore an object of this invention to provide an apparatus for growing a semiconductor crystal and a method of growing the same in which no contaminated impurity is mixed from an electrode into semiconductor melt (or solution).
It is another object of this invention to provide an apparatus for growing a semiconductor crystal and a method of growing the same in which rotation symmetry of semiconductor melt is not degraded.
According to this invention, a crucible holds a semiconductor melt. Further, an electrode contacts the semiconductor melt and applies a current to the semiconductor melt. With such an arrangement, the electrode is formed of the same material as the semiconductor crystal.
In this case, a magnetic field is applied to the semiconductor melt in addition to the current. The magnetic field is substantially perpendicular to the current. Herein, the current is applied between the semiconductor melt and the semiconductor crystal.
Moreover, a predetermined impurity is doped into the semiconductor crystal from the semiconductor melt. Under this circumstance, the semiconductor crystal does not contain the other impurity except for the doped impurity.
In this case, the semiconductor crystal may be a silicon single crystal, and the electrode is formed by the silicon single crystal. Under this circumstance, a predetermined impurity and oxygen are doped into the silicon single crystal from the semiconductor melt. In this case, the silicon single crystal does not contain the other impurity except for the doped impurity and the oxygen.
Alternatively. the semiconductor crystal may be a GaAs single crystal. In this case, the electrode is formed of GaAs single crystal.
Further, the semiconductor crystal may be an InP single crystal. In this case, the electrode is formed of InP single crystal.
More specifically, when current is applied or supplied between the semiconductor melt and the semiconductor crystal during growth, the same material as the semiconductor crystal to be grown is used as the electrode.
Consequently, no impurity is mixed from the electrode into the semiconductor melt, and further, unnecessary impurity is not mixed into the growing semiconductor crystal.
Further, the electrode contacts with the semiconductor melt at a position above the main surface of the semiconductor melt. As a consequence, the rotation of the semiconductor melt is not disturbed by the electrode. As a result, the rotation of the semiconductor melt is not degraded.
Thereby, the symmetry of the axis of temperature distribution is enhanced, and concentration distribution of the dopant impurity trapped or doped in the semiconductor crystal becomes uniform in a radial direction.
Moreover, the concentration distribution of oxygen can be further equalized in the radial direction in the case of the silicon single crystal.